Uninterruptible power supply (UPS) systems may be used for supplying power to various loads such as data centers. Such a system may then comprise a number of parallel UPS branches connected between a ring bus and a power supply cable connected to a power distribution system or grid. Each such branch may furthermore comprise an UPS module and supply power to a corresponding load, where an UPS module may comprise series-connected magnetically coupled reactors separated by a tap point and an auxiliary power supply connected to the tap point. An UPS unit may thus be based on an autotransformer. In such a system it is also possible that various entities are interconnected using cables.
In relation to such a power supply a fault may occur in the ring bus, in a load, in the power supply cable, or even in the grid. In order to isolate the fault from the rest of the power supply system, one or more circuit breakers may also be provided and these circuit breakers may be vacuum circuit breakers.
However, if the circuit breaker is a vacuum circuit breaker, then the opening of it may lead to high transient voltages at the various inductive elements of the power supply system, such as at reactors between cable sections and the above-described autotransformer of the UPS module. One or more of these inductive elements may therefore need to be protected from such overvoltages caused by the operation of such vacuum circuit breakers.
A commonly used type of protective component is a surge arrester. Surge arresters are for instance known to be used for protecting transformers, such as dry type transformers, see for instance EP 3023998 and US 2016/0149396.
However, surge arresters have also been known to be used in other environments. US 2013/0321959 does for instance disclose a power supply converter unit where surge arresters are connected between phases as well as between phase and ground before and after an inductor in order to protect the inductor.
U.S. Pat. No. 5,388,021 discloses a power supply connected to a load via a circuit breaker and an inductor. Surge arresters are connected to ground on both sides of the inductor. There is also a surge arrester connected in parallel with the inductor.
KR 2012 0097359 discloses a power saver for a lamp. A power supply is connected to a load via a capacitor in parallel with a reactor. There is also a surge absorber connected between the reactor and ground.
US 2011/0279943 discloses a surge suppressor device with an input connected to an output via a capacitor in parallel with two inductors. There is also a gas tube connected between one end of the parallel connection and ground, which gas tube may be replaced by a metal oxide varistor.
U.S. Pat. No. 5,532,897 discloses a surge suppression system for a high voltage substation, where two surge arresters are connected on opposite sides of a reactor. There is also a resistor connected in parallel with the reactor. Faults which are disconnected through vacuum circuit breakers may not only occur on the supply side of the inductive element but also on the load side. It would therefore be of interest to protect an inductive element of a power supply system against overvoltages that may occur on both sides of the inductive element.